Electrolytic production of pure tin.



UNiTED STATES- PATENT OFFICE.

ADOLPHE JEAN MARIE THIROT, OF BOURGES, FRANCE, ASSIGNOR TO HIMSELF, AND LOUIS AUGUSTE MAGE, OF AVIGNON, ERANCE.

ELECTROLYTIC PRODUCTION OF PURE TIN.

Specification of Letters Patent.

Patented umn'si, 19.08.

Application filed larch 22, 1907. Serial No. 363,900.

To all whom it ma'y concern;

Be it known that I, ADOLPHE J EAN MARIE Tumor, of 83 Rue Bourbonnoux, Bourges,

pre aration, as energetic oxidizing roasting.

an lixiviation, or again from all products capable of yielding stannate of soda, by the wet or the igneous process, such as tin drosses, tin work waste or old tin late.

If the product treated IS'bIOllZG, nearlyall of the tin derived therefrom is found in the form of stannous hydrate, which it is advisable to preliminarily transform into stannic hydrate.

This oxidation takes place after washing the slimes, being effected naturally, at the surrounding temperature, in the course of exposure of the slimes to the air, with a view'to their'desiccation, by atmols pheric action.

e impurities found, will always be constituted, whatever the origin of the product operated upon, by hydroxids, oxids, sulfates, arsenites, arseniates, antimonites, antimoni:

ates, of. common metals, such as copper,

lead, iron, bismuth, &c. In the case of slimes resulting from bronze, there mi h-t be found appreciable traces of silver and 0 gold.

If the product treated is tin work waste, or-

tin dross, it will contain as impurities principalli iron, lead and cop r. A

T e process which forms the object of the invention, comprises three principal-operations, first, the formation of a solution of stannate of soda; second, purification of this solution; and third, electrolysis of the solu tion.

To obtain the solution of stannate of soda, when dealin with hydroxids of tin, they are treated at t e boiling point, with a ten or twelve per cent. solution of caustic soda,in iron vessels, basing the process on the fact that one liter of a twelve per cent. sodic solution can dissolve from 45 to 50grarns of tin..

I indicated. -After electrolysis, the liquid will yet contain a certain proportion of stannate tinper liter.

To obtain the solution of stannate of soda, it is necessary to retain the mixture at the boiling point. for about one and one-half hours, stirring it during ebullition. A To facilitate the operation, several vessels are ordinarily employed, and a methodical liquid passing successively from one vessel to the other.

- If the product treated .is tin oxids or metallic tin partly oxidized (tin dross, tin 'work waste, &c), instead of tin hydroxid, the same process may be employed, but the formation of the stannate is more diihcult, and it may j be necessary in certain cases to form the f stannate of soda by the igneous process and !.then dissolve it. 3

Except tin, there enters into the solution,

an of these meta s copper and lead are the only ones whose presence causes difficulty. Antimony for the major part, enters into solution in the form of antimonite ofsoda, but in the course of electrolysis, under the action of ox gen which is disengaged at the anodes an under the action of the temperature of the. electrolyte, this salt is transformed into antimoniate of soda, which is deposited in the first vats or vessels of the series durin the electrolysis; on account of its insolubility in the sodic li uor. Arsenic forms arsenite and arseniate o soda, both of which are soluble. Arsenite is converted into arseniate in the same manner as the antimonite is converted into the antimoniate.

in the sodic liquor and hence accumulates in the liquor.

The precious metals remain inthe waste, which may constitute a subroduct some what strongly argen'tiferoils rf.the roduct treated is constituted by slimes o tained from bronze by electrolysis.

cation of the stannate solution, and 1s carriedv out while hot, about 70 centigrade in any other suitable manner. When the solution is at the proper tem erature, sodium sulfid is added, monos ds in preference to polysulfids, by which copper enrichment of the liquor is practiced, the- The arseniate however does not electrolyze The second operation consists in the urifi- V of soda corresponding .to -ab'out ten gramsof =onl very small uantities of'othermetals,

usually, in an iron vessel heated by steam, or

collected and filtered, constitutin and lead are precipitated. In ractice a very concentrated solution of so ium sulfid is made use of, the amount necessary to add being approximately determined beforehand, by adding a known amount of sodium sulfid to a sample of the solution, filtering, and adding more sodium sulfid to the. filtrate. When no precipitate appears in the filtrate the proper amount of sodium sulfid has been determined. A slight excess of sodium sulfid is however immaterial.

The liquor should be well stirred during the addition of the sulfid. Afterthe adding of the sulfid, the liquid is permitted to clarify andis decanted. The precipitate may be a subproduct whose composition depen s on the primitive materials employed. The mother waters which are rich 1n stannates of soda are also collected.

The electrolysis of the urified solution maybe effected in iron ta s with insoluble anodes of iron and cathodes of sheets of tin or even .of tin plate. It is important to maintain the solution during the electrolyzing at a minimum temperature of 80 degrees centigrade, and if steam circulation is employed for the heating it will of course be necessary to guard against the steam pipes placing the vats in s ort circuit with each other. This end may be attained by threadin on the tubing short lengths of tubes of ins ating material, caoutchouc for example.

The voltage necessary to electrolyze the solution will be about 2.4 volts with an amperage of 300 to 400 per s uare me'ter of cathode, a single side only eing counted. Twenty-five, vats may be easily placed in series, one being limited in this respect only by difficulties of insulation, .WhlOlfl commences to arise when the total voltage ex- .ceeds approximately sixty volts.

In the present process, the electrolysis is effected under the following essential conditions necessary to obtain a good deposit.

1st. The temperature of the electrolyte should be maintained as high as possible, at the least at 80 degrees centigrade;

2nd. An excessive amperage of current should be avoided;

3rd. Theelectrolyte should be maintained sufficiently concentrated in stannate of soda;

4th. The electrolyte should be maintained in a fairly active circulation;

5th. Insoluble anodes should be employed.

The third condition re uires'that the solution be not exhausted y electrol sis, the concentration below which a goo deposit cannot be easily obtained bemg approximately ten grams of tin per liter. A good arrangement for this purpose consists in arranging the apparatus so that the electrolyte circulates from one vat to another through tubes of caoutchouc, grouping the vats into one or several series in each of which they are arranged cascade-wise.

The rich liquor proceeding from the purification is introduced into the upper vats and the speed of circulation is regulated so that the concentration is a little above the minimum concentration permitting the obtaining of a good deposit. In practice the speed of circu ation,of the electrolyte is diminished until the deposit of tin on the cathodes of the lower vats commeces to become slightly black.

It is advisable to compensate for evaporation by a continuous addition of water in certain proportion into the liquid which leaves the lower vats, so that the quantity of free or combined soda per liter be restored to the same proportion as at the commencement. Bymeans of the above precautions and a regular conduct of the operation, there can be obtained an excellent deposit of tin of a clear gray color very adherent and coherent and comparable to the electrolytic deposits of copper. If the bodies of the cathodes are of pure tin, the cathodes can be stored or enter into commerce, after a simple washing in water as hot as possible.

In cases Where cathodes oftin plate are employed, they can after washin and drying, be-very readily cleared of t e tin de in fusion. The'surplus tin fuses, and the bodiesremain tinned and are capable of servin anew.

y the above process tin can be obtained containing less than a thousandth of impurities.

The quantity of tin per ampere-hour may attain to 0. 8 grams, when the amperage is not too strong; but when it is desired to raise the amperage, the voltage is raised, the

Water commences to be electrolyzed, and the yield is less.

The process presents economic superiority over existing methods of electro-deposition of tin, in that there may be obtained by direct deposit upon the cathodes pure tin in the form of adherent and coherent metal. Con- 'sequently the increase of expense for electric energy, due to the employment of insoluble anodes and to the fact that the quantity of tin deposited per ampere-hour is rather small, is largely compensated by the suppression. of operations consecutive to the electrolysis and necessary in old processes, such operations consisting in washings of spon y precipitates, a glomeration by liydrau ic pressure, and sion, during which processes important losses take place due to oxidation, and in addition a spon y metal even after agglomeration is the resuIt.

The electrolyte slightly carbonates under the action of the carbonic acid of the air durin the manipulations to which it is subjecte but this carbon does not in any way "posit, by asimple immersion in a bath of tin hinder the operation even when it is very ap- On the other hand if the primi reusing. During this cooling, the excess of.v sulfate and carbonate crystal iz es and can be collected.

I claim 4 1'. A method for producing pure tin, which consists in treating the tin compound with boiling caustic soda to form sodium stannate, purifying the sodium stannate by the addition of concentrated sodium sulfid, separatin the precipitate from the solution and su jecting the solution to electrolysis.

2. A method for producing pure tin from its compounds which consists in treating the tin com ounds with boiling causticsoda, purifying t e resulting sodium stannate and subjecting the solution to electrolysis. I

3. A, method for obtaining tin from its compounds which consists in' treating the compounds with caustic soda, purifying the solution and subjecting the solution to electrolysis.

4. A method for obtaining tin from its compounds,. which consists in treating the compounds with caustic soda to form sodium stannate, pur' ing the solution, and subjecting the so ution to electrolysis while maintaining the electrolyte at at least 80 centigrade.

5. A method for obtaining tin from its compounds, which consists in treating the compounds with caustic soda,'purifying thesolution, and subject-ing the solution to electrolysis, with a current of 300 to 400 amperes persquare meter of anode surface. 4

he foregoing specification of my electro ytic product-ion of pure tin signed by me this 12th day of March; 1907;

' ADOLPHE JEAN MARIE THIROT. Witnesses:

HERNANDO DE So'ro, MApRIoE H. PIGNEAT. 

